investigation on effect of tig welding parameters on
TRANSCRIPT
Sigma Journal of Engineering and Natural Sciences, Vol. 39, No. 1, pp. 80-96, March, 2021 Yildiz Technical University Press, Istanbul, Turkey
This paper was recommended for publication in revised form by Regional Editor Ayşegül Akdoğan Eker 1 Research Scholar, Department of Mechanical Engineering, Andhra University, Visakhapatnam, India
2 Professor, Department of Mechanical Engineering, Andhra University, Visakhapatnam, India
* E-mail address: [email protected] Orcid id: https://orcid.org/0000-0002-0905-9688 Manuscript Received 18 April 2020, Accepted 23 December 2020
INVESTIGATION ON EFFECT OF TIG WELDING PARAMETERS ON DISSIMILAR WELD JOINTS OF AISI 304 AND AISI 310 STEELS USING
RESPONSE SURFACE METHOD
Rami Reddy PADALA V.1,*
, Kesava RAO V. V. S.2
ABSTRACT Dissimilar weld joints plays a major role in power generation, electronic, nuclear reactors, petrochemical
and chemical industries due to environmental concerns, energy saving, high performance, cost saving and so on.
However efficient welding of dissimilar metals has posed a major challenge due to difference in thermal, mechanical
and chemical properties of the materials to be joined under a common welding condition. In the present work
dissimilar joints of AISI 304 and AISI 310 steels are produced using Tungsten Inert Gas (TIG) welding. Welding
current, wire feed rate, flow rate of gas and edge included angle are considered as input parameters and tensile
strength, Impact strength and Maximum bending load are considered as output responses. Response Surface Method
(RSM) is adopted using Central Composite Design (CCD) and 31 experiments were performed for 4 factors and 5
levels. Tensile strength, impact strength and maximum bending load are measured. Analysis of Variance (ANOVA) is
carried out at 95% confidence level. Effect of welding parameters on output responses are studied by drawing main
effect plots, contour plots and surface plots. Optimal weld parameters are identified using Response optimizer
Keywords: Dissimilar welds, AISI 304, AISI 310, steels, TIG welding
INTRODUCTION In Welding is a joining process in which we can make permanent joint at contacting surfaces of metals,
alloys or plastics by application of heat and or pressure. In welding, the work-pieces are melted at the interface and
after solidification a permanent joint at interface can be achieved. In some welding a filler material is added for
forming weld pool of molten material, which after solidification provides a strong bond between the materials. The
ability of a material to be welded is known as weldability of a material and it depends on different factors like
melting point of metal, thermal conductivity, reactivity of material with surrounding, material’s coefficient of thermal
expansion etc.
Metallurgy of a welded joint Metal is heated over the range of temperature up to fusion and followed by cooling ambient temperature.
Due to differential heating, the material away from the weld bead will be hot but as the weld bead is approached
progressively higher temperatures are obtained, resulting in a complex micro structure. The subsequent heating and
cooling results in setting up internal stresses and plastic strain in the weld.
A joint produced without a filler metal is called autogenously and its weld zone is composed of re-solidified
base metal. A joint made with a filler metal is called weld metal. Since central portion of the weld bead will be
cooled slowly, long columnar grains will developed and in the out ward direction grains will become finer and finer
with distance.
So the ductility and toughness decreases away from the weld bead. However strength increases with the
distance from the weld bead. The original structure in steels consisting of ferrite and pearlite is changed to alpha iron.
The weld metal in the molten state has a good tendency to dissolve gases which come into contact with it like
oxygen, nitrogen and hydrogen.
So during solidification, a portion of these gases get trapped into the bead called porosity. Porosity is
responsible for decrease in the strength of the weld joint. Cooling rates can be controlled by preheating of the base
metal welding interface before welding. The heat affected zone is within the base metal itself. It has a microstructure
different from that of the base metal after welding, because it is subjected to elevated temperature for a substantial
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period of time during welding. In the heat affected zone, the heat applied during welding recrystallizes the elongated
grains of the base metal, grains that are away from the weld metal will recrystallizes into fine equiaxed grains.
Dissimilar welding Joining of dissimilar metals has found its use extensively in power generation, electronic, nuclear reactors,
petrochemical and chemical industries mainly to get tailor made properties in a component and reduction in weight.
However efficient welding of dissimilar metals has posed a major challenge due to difference in thermo-mechanical
and chemical properties of the materials to be joined under a common welding condition. This causes a steep
gradient of the thermo-mechanical properties along the weld.
A variety of problems come up in dissimilar welding like cracking, large weld residual stresses, migration of
atoms during welding causing stress concentration on one side of the weld, compressive and tensile thermal stresses,
stress corrosion cracking, etc. Now before discussing these problems coming up during dissimilar welding, the
passages coming below throw some light on some of the causes of these problems.
In dissimilar welds, weldability is determined by crystal structure, atomic diameter and compositional
solubility of the parent metals in the solid and liquid states. Diffusion in the weld pool often results in the formation
of intermetallic phases, the majority of which are hard and brittle and are thus detrimental to the mechanical strength
and ductility of the joint.
The thermal expansion coefficient and thermal conductivity of the materials being joined are different,
which causes large misfit strains and consequently the residual stresses results in cracking during solidification.
Atul Kumar et al.[1] studied the strength of the welds of SS202 and SS410 stainless steel of 3mm thick
using Taguchi Method. Welding current, gas pressure and weld rate are considered as input welding parameters.
Iqbaljeet Singh Grewal et al.[2] studied tensile strength and impact toughness of the welded joints using Taguchi
method using Welding current, gas flow rate and filler metal are considered in their study. Owunna1 and A. E.Ikpe
[3] investigated Ultimate Tensile Strength, modulus of elasticity ,elongation and strain for twenty samples of AISI
4130 Low carbon steel plate. Mukesh Hemnani et al. [4] carried out bead on bar welds on EN8 & EN24 solid
cylindrical bar using Tungsten Inert Gas (TIG) welding process. Taguchi method is adopted by considering welding
current, welding voltage & gas flow rate as welding parameters K. Nageswara Rao et al. [5] studied a variety of
problems come up in dissimilar welding like cracking, large weld residual stresses, migration of atoms during
welding causing stress concentration on one side of the weld, compressive and tensile stresses, stress corrosion
cracking. Baljeet Singh et al. [6] studied the influence of welding parameters on weld-ability of both stainless steel
304 and mild steel 1018 specimens .Welding voltage, welding speed and gas flow rate are considered. S. Mohan
Kumar and N. Siva Shanmugam [7] studied the weldability, mechanical properties and microstructural
characterization of activated flux TIG welding of AISI 321 austenitic stainless steel. Effect of Activated Tungsten
Inert gas (A-TIG) welding on the surface morphology of type 321 austenitic stainless steel welds are SS compared
with conventional TIG welding.
G. Venkatesan et al. [8] studied the effect of ternary fluxes viz. SiO2, TiO2 and Cr2O3 on depth of
penetration in A-TIG welding of AISI 409 ferritic stainless steel. Mukesh and Sanjeev Sharma [9] analysed the
mechanical properties in austenitic Stainless steel using Gas Tungsten Arc Welding (GTAW) and the influence of
different input parameters such as welding current, gas flow rate and welding speed on the mechanical properties
during the gas tungsten arc welding of austenitic stainless steel 202 grade. Salah Sabeeh Abed Alkareem [10]
compared heat flux generated during welding with and without fillers. The study covered the effect of welding
current, welding time, welding velocity, gas flow from cylinder, gas flow before welding and gas flow on the
generated heat flux during this comparison.
The objective of the paper is to study the effect of TIG welding parameters on tensile strength, impact
strength and maximum bending load of dissimilar joints of AISI 304 and AISI 310 steels.
EXPERIMENTATION AISI 304 and AISI 310 plates of 5 mm thickness were chosen for welding. First the plates were cut into
100mm x 200mm X 5mm size using shearing machine and cleaned by using Ultrasonic cleaning and further cleaned
with PCL 21 cleaner before welding. Copper sinks are fixed to the fixture to minimize weld distortion and extreme
care has been taken for proper cutting of plates. Details about weld joint dimensions are shown in Figure 1.
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Figure 1. Dimensions of welded joint
The chemical composition and tensile properties of AISI 304 and AISI 310 steel plates are given in Table .1
to 4. The welding has been carried out under the welding conditions presented in Table 5. From the earlier works
carried out on TIG welding, it was understood that the Welding Current, welding speed, flow rate of gas and edge
included angle are the dominating parameters which effect the weld quality characteristics. The range of the welding
parameters are chosen based on trial experiments and from earlier works reported [11-16] are presented in Table .6.
Tensile specimens are prepared as per ASTM E8M-04 guidelines using wire cut Electro Discharge
Machining in the transverse direction of the weld from each welded sample. Tensile tests are carried out on 100 KN
computer controlled Universal Testing Machine (Model No: 8801, INSTRON). The specimen is loaded at a rate of
1.5 KN/min as per ASTM specifications, so that the tensile specimens undergo deformation. From the stress strain
curve, the ultimate tensile strength of the weld joints is evaluated and the average of the results of each sample is
presented in Table .7. Charpy Impact testing was performed on the weld specimens as per ASTM E23-18. Impact
strength per unit volume is measured. Tests were carried out on Three readings are taken for each sample and the
average values are reported in Table.7. Bending test is performed as per ASTM E855-08 on the weld samples. Tests
were carried out on 1000 Ton capacity TUE-C-1000, FSA (Fine Spavy Associate Pvt Ltd) machine. The maximum
bending load is recorded for each weld sample and presented in Table.7.
Table 1. Chemical composition of AISI 304 (weight %)
Element Cr Mn Fe Ni Cu Mo
Weight % 18.09 1.72 71.46 7.92 0.45 0.36
Table 2. Mechanical properties of AISI 304
Property Ultimate Tensile Strength Yield Tensile Strength Vickers Hardness
Value 505 MPa 215 MPa 210
Table 3. Chemical composition of AISI 310 (weight %)
Element Cr Mn Fe Ni Mo
Weight % 25.28 0.43 53.94 20.32 0.029
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Table 4. Mechanical properties of AISI 310
Property Ultimate Tensile Strength Yield Tensile Strength Vickers Hardness
Value 520 MPa 270 MPa 225
Table 5. Welding conditions
Power source ESAB TIG 400i
Polarity DCEN
Mode of operation Continuous mode
Filler wire material AISI 309
Filler wire diameter 2.4mm
Welding Gas Argon
Electrode Tungsten (2% Thoriated)
Electrode Diameter 2 mm
Torch Position Vertical
Operation type Semi Automatic
Table 6. Input parameters
PARAMETER Level
-2 -1 0 +1 +2
Welding Current(Amperes) 140 150 160 170 180
Gas Flow rate (litres/min) 8 10 12 14 16
Welding Current (mm/min) 120 140 160 180 200
Edge Included Angle (Degrees) 30 40 50 60 70
STATISTICAL ANALYSIS Using MINTAB statistical software design matrix is generated for 4 factors, 5 levels and welding is carried
out for all the 31 combination of welding parameters and the values recorded for various tests performed are
presented in Table.7
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Table 7. Experimental values
Input Parameters Output Responses
Experimental Predicted
Exp.No. Welding
Current
(Amps)
Flow rate
of gas
(litres/min)
Welding
speed
(mm/min)
Edge
Included
Angle
(Deg)
Tensile
Strength
(MPa)
Impact
Strength
(Joules)
Max.
Bending
Force
(KN)
Tensile
Strength
(MPa)
Impact
Strength
(Joules)
Max.
Bending
Force
(KN)
1 150 10 140 40 594.13 74 4.6 594.504 75 4.6
2 170 10 140 40 591.08 71 4.6 593.127 73 4.6
3 150 14 140 40 593.42 73 4.7 593.293 73 4.7
4 170 14 140 40 595.13 75 4.5 593.171 73 4.5
5 150 10 180 40 594.25 74 4.6 592.293 72 4.6
6 170 10 180 40 596.46 76 4.7 595.666 75 4.7
7 150 14 180 40 580.79 61 4.5 581.333 61 4.5
8 170 14 180 40 584.75 65 4.4 585.96 66 4.5
9 150 10 140 60 589.75 70 4.3 588.127 68 4.3
10 170 10 140 60 592.96 73 4.5 590.999 71 4.5
11 150 14 140 60 596.29 76 4.6 595.666 76 4.6
12 170 14 140 60 598.25 78 4.7 599.793 80 4.7
13 150 10 180 60 593.63 74 4.2 594.171 74 4.2
14 170 10 180 60 602.08 80 4.5 601.793 81 4.5
15 150 14 180 60 594.42 74 4.4 591.96 72 4.4
16 170 14 180 60 602.63 83 4.7 600.838 81 4.7
17 140 12 160 50 590.79 71 4.7 592.541 73 4.7
18 180 12 160 50 599.96 80 4.9 600.041 80 4.9
19 160 8 160 50 592.46 72 4.3 593.374 73 4.3
20 160 16 160 50 590.29 70 4.5 591.208 71 4.5
21 160 12 120 50 590.63 71 4.9 590.879 71 4.9
22 160 12 200 50 588.13 68 4.8 589.713 69 4.8
23 160 12 160 30 590.63 71 4.2 590.046 70 4.2
24 160 12 160 70 596.13 76 4 598.546 78 4
25 160 12 160 50 594.86 75 4.5 595.717 76 4.6
26 160 12 160 50 594.86 75 4.5 595.717 76 4.6
27 160 12 160 50 594.86 75 4.5 595.717 76 4.6
28 160 12 160 50 594.86 75 4.6 595.717 76 4.6
29 160 12 160 50 596.86 77 4.6 595.717 76 4.6
30 160 12 160 50 594.86 75 4.7 595.717 76 4.6
31 160 12 160 50 598.86 78 4.5 595.717 76 4.6
Empirical Mathematical Modelling A second order polynomial is some region of the independent variables is employed to develop a relation
between the response and the independent variables. If the response is well modeled by a nonlinear function of the
independent variables then the approximating function in the second order model is
Y = bo+bixi +biixi2 + bijxixj+ (1)
Where bo, bi are the coefficients of the polynomial and represents noise
using MINTAB software by considering the nonlinear model empirical models are developed by considering
only the significant coefficients.
Tensile strength = 769.226-1.941X1+6.640X2+0.335X3-4.096X4-0.214X22-0.003X3
2
+0.006X1X3+0.011X1X4 -0.061X2X3+0.109X2X4+0.010X3X4 (2)
Impact Strength = 244.923-1.888X1+4.744X2+0.421X3-3.879X4-0.21222-0.003X3
2
+0.005X1X3 -0.058X2X3+0.116X2X4+0.010X3X4 (3)
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85
Max. Bending Load = 26.8091-0.2270X1+0.4326X2-0.0733X3-0.0430X4+0.0006X12
-0.0101X2
2 +0.0002X3
2 -0.0012X4
2 +0.0016X1X2
+0.0002X1X3 +0.0007X1X4 - 0.0008X2X4+0.0041X3X4 (4)
where X1, X2 , X3, X4 represents the coded values of welding current, gas flow rate, welding speed and edge
included angle.
Analysis of Variance (ANOVA) The adequacy of the developed models is tested using the ANOVA. As per this technique, if the calculated
value of the Fratio of the developed model is less than the standard Fratio (F-table value 2.56) value at a desired level of
confidence of 95%, then the model is said to be adequate within the confidence limit. ANOVA test results are
presented in Table .8 for tensile strength, impact strength and maximum bending load. From table 8 it is understood
that the developed mathematical models are found to be adequate at 95% confidence level. Coefficient of
determination ‘ R2’ for the above developed models is found to be above 0.90. The variation of Experimental and
predicted values are presented in Scatter plots as shown in figure 2 to 4.
Table 8. ANOVA Table
Tensile strength
Source DF Seq SS Adj SS Adj MS F P
Regression 14 555.60 555.60 39.686 10.30 0.000
Linear 4 201.83 86.51 21.628 5.61 0.005
Square 4 71.80 71.80 17.949 4.66 0.011
Interaction 6 281.97 281.97 46.995 12.20 0.000
Residual Error 16 61.64 61.64 3.853
Lack-of-Fit 10 46.64 46.64 4.679 1.89 0.225
Pure Error 6 14.86 14.86 2.476
Total 30 617.24
Impact Strength
Source DF Seq SS Adj SS Adj MS F P
Regression 14 521.64 521.64 37.260 10.37 0.000
Linear 4 184.87 73.37 19.092 5.31 0.006
Square 4 70.85 70.85 17.714 4.93 0.009
Interaction 6 265.91 265.91 44.319 12.34 0.000
Residual Error 16 57.48 57.48 3.593
Lack-of-Fit 10 47.40 47.40 4.740 2.82 0.109
Pure Error 6 10.09 10.09 1.681
Total 30 579.12
Max. Bending Load
Source DF Seq SS Adj SS Adj MS F P
Regression 14 1.14057 1.14057 0.081469 24.61 0.000
Linear 4 0.15500 0.22197 0.055494 16.76 0.000
Square 4 0.75682 0.75682 0.189206 57.14 0.000
Interaction 6 0.22875 0.22875 0.038125 11.51 0.000
Residual Error 16 0.05298 0.05298 0.003311
Lack-of-Fit 10 0.01583 0.01583 0.001583 0.26 0.972
Pure Error 6 0.03714 0.03714 0.006190
Total 30 1.19355
where SS= Sum of Squares, MS= Mean Squares, F=Fishers value
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Figure 2. Scatter plot for tensile strength
Figure 3. Scatter plot for impact strength
Figure 4. Scatter plot for Max. Bending Load
Predicted
Exp
eri
me
nta
l
605600595590585580
605
600
595
590
585
580
Scatterplot of Tensile Strength(MPa)
Predicted
Exp
eri
me
nta
l
858075706560
85
80
75
70
65
60
Scatterplot of Impact Strength(Joules)
Predicited
Exp
eri
me
nta
l
4.94.84.74.64.54.44.34.24.14.0
4.9
4.8
4.7
4.6
4.5
4.4
4.3
4.2
4.1
4.0
Scatterplot of Max.Bending Load(KN)
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87
Main effect plots Main effects of tensile strength, impact strength and maximum bending load are presented in Figure 5, 6 and
7.
Figure 5. Main Effects of tensile strength
As welding current increases, heat input increases and the filler metal melts faster leading to faster
deposition of filler metal in the weld group leading to higher tensile strength of the welded joint. As flow rate of the
welding gas increases the burning capacity increases because of higher amount of gas available, however when the
gas flow rate of gas reaches 12 litres/min the filler wire will melt fast and the same time it spills on the outer side of
the weld grove leading to poor weld joint and lower tensile strength. Welding speed plays an important role in getting
the desired quality. Low welding speeds leads to over melting and higher welding speeds leads to improper
penetration. At 160 mm/min optimal welding speed is achieved. While joining thick plate, edge include angle is
critical as it decides how much filler material it can accommodate. Higher angle leads to less penetration, whereas
lower angle leads to more penetration for same welding speed. Hence optimal edge included angle is important
which decides the strength. At edge included angle of 60 Deg optimum tensile strength is obtained.
Figure 6. Main effects of impact strength
Me
an
of
Te
nsile
Str
en
gth
(MP
a)
180170160150140
600
597
594
591
588
161412108
200180160140120
600
597
594
591
588
7060504030
Welding Current(Amps) Gas Flow Rate(Litres/min)
Welding Speed(mm/min) Edge Included Angle(Deg)
Main Effects Plot (data means) for Tensile Strength(MPa)
Me
an
of
Imp
act
Str
en
gth
(Jo
ule
s)
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81
78
75
72
69
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200180160140120
81
78
75
72
69
7060504030
Welding Current(Amps) Gas Flow Rate(Litres/min)
Welding Speed(mm/min) Edge Included Angle(Deg)
Main Effects Plot (data means) for Impact Strength(Joules)
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88
Impact strength of the welded joint improves with welding current because at higher current more heat ,
which helps in faster melting of filler wire and high deposition rate. Flow rate of welding gas has negative impact on
impact strength. Higher flow rates may create blow holes and other defects, which decreases the impact strength.
Impact strength improves with welding speed up to 160 mm/min and there after it decreased, this may be due to
improper penetration of filler metal. While joining thick plate, edge include angle is critical as it decides how much
filler material it can accommodate. Higher angle leads to less penetration, whereas lower angle leads to higher
penetration. Hence optimal edge included angle is important which decides the strength. At 60 Deg angle maximum
impact strength is noticed, there after the strength remained constant.
Figure 7. Main effects of Max. Bending Load
Bending load is minimum at welding current of 160 Amps, there after it increased, this may be due to proper
fusion of filler metal at higher heat input because of high current. Gas flow rate along with high welding current
improves the deposition rate of the filler metal, hence higher bending load. However beyond 12 litres/min, bending
load tends to decrease because of violent agitation of molten metal. Bending load decreased with welding speed up to
160 mm/min and there after it increased. The increase in bending load is due to higher penetration of filler metal.
Higher Bending load was observed at edge include angle of 50 Deg and there after it decreased, this may be due to
incomplete penetration of filler metal because of wider angle.
Contour plots The simultaneous effect of two parameters at a time on the output response is generally studied using
contour plots. Contour plots play a very important role in the study of the response surface. By generating contour
plots using statistical software (MINITAB 14) for response surface analysis, the most influencing parameter can be
identified based on the orientation of contour lines. If the contour patterning of circular shaped occurs, it suggests the
equal influence of both the factors; while elliptical contours indicate the interaction of the factors. Figure 8 to 10
represents the contour plots for tensile strength, impact strength and maximum bending load.
Me
an
of
Ma
x.B
en
din
g L
oa
d(K
N)
180170160150140
4.8
4.6
4.4
4.2
4.0
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200180160140120
4.8
4.6
4.4
4.2
4.0
7060504030
Welding Current(Amps) Gas Flow Rate(Litres/min)
Welding Speed(mm/min) Edge Included Angle(Deg)
Main Effects Plot (data means) for Max.Bending Load(KN)
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89
Figure 8(a). Figure 8(b).
Figure 8(c).
Figure 8. Contour plots for tensile strength
From Fig.8(a) it is clear that welding current is dominating over gas flow rate.
From Fig.8(b) it is clear that welding current is dominating over edge included angle.
From Fig.8(c) it is clear that welding current is dominating over welding speed.
Welding Current(Amps)
Ga
s F
low
Ra
te(L
itre
s/
min
)
180170160150140
16
14
12
10
8
Contour Plot of Tensile Strength
Welding Current(Amps)
Ed
ge
In
clu
de
d A
ng
le(D
eg
)
180170160150140
70
60
50
40
30
Contour Plot of Tensile Strength
Welding Current(Amps)
We
ldin
g S
pe
ed
(mm
/m
in)
180170160150140
200
180
160
140
120
Contour Plot of Tensile Strength
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90
Figure 9 (a). Figure 9(b).
Figure 9 (c).
Figure 9. Contour plots for impact strength
From Fig.9(a) it is clear that welding current is dominating over gas flow rate.
From Fig.9(b) it is clear that welding current is dominating over edge included angle.
From Fig.9(c) it is clear that welding current is dominating over welding speed.
Welding Current(Amps)
Ga
s F
low
Ra
te(L
itre
s/
min
)
180170160150140
16
14
12
10
8
Contour Plot of Impact Strength
Welding Current(Amps)
Ed
ge
In
clu
de
d A
ng
le(D
eg
)
180170160150140
70
60
50
40
30
Contour Plot of Impact Strength
Welding Current(Amps)
We
ldin
g S
pe
ed
(mm
/m
in)
180170160150140
200
180
160
140
120
Contour Plot of Impact Strength
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91
Figure 10(a). Figure 10(b).
Figure 10(c).
Figure 10. Contour plots for maximum bending load
From Fig.10(a) it is clear that welding current is dominating over gas flow rate.
From Fig.10(b) it is clear that welding current is dominating over edge included angle.
From Fig.10(c) it is clear that welding current is dominating over welding speed.
From the contour plots(Fig.8, 9 and 10), it is understood that the most dominating parameter is welding
current, followed by welding speed, flow rate of gas and edge included angle.
Surface plots Surface plots are drawn to identify the optimal values of welding parameters. The apex and nadir of the
surface plot represent maximum and minimum values of the output response.
Figure 11 to 13 indicates the surface plots for tensile strength, impact strength and Max. Bending load. The
objective is to maximize tensile strength, impact strength and Max. Bending load. From the surface plots one can
find the optimum value by considering two parameters at a time.
Welding Current(Amps)
Ga
s F
low
Ra
te(L
itre
s/
min
)
180170160150140
16
14
12
10
8
Contour Plot of Max.Bending Load
Welding Current(Amps)
Ed
ge
In
clu
de
d A
ng
le(D
eg
)
180170160150140
70
60
50
40
30
Contour Plot of Max.Bending Load
Welding Current(Amps)
We
ldin
g S
pe
ed
(mm
/m
in)
180170160150140
200
180
160
140
120
Contour Plot of Max.Bending Load
Sigma Journal of Engineering and Natural Sciences, Research Article, Vol. 39, No. 1, pp. 80-96, March, 2021
92
Figure 11(a). Figure 11(b).
Figure 11 (c).
Figure 11. Surface plots for tensile strength
From Fig.11(a) it is understood that maximum tensile strength is obtained at welding current of 140 Amps
and welding speed of 200 mm/min.
From Fig.11(b) it is understood that maximum tensile strength is obtained at welding current of 140 Amps
and edge included angle of 60 Deg.
From Fig.11(c) it is understood that maximum tensile strength is obtained at welding current of 140 Amps
and gas flow rate of 16 litres/min.
From surface plots of tensile strength (Figure.11), it is understood that maximum tensile strength is obtained
at welding current of 140 Amps, gas flow rate of 16 litres/min, welding speed of 200 mm/min and edge included
angle of 60 Deg.
590
600
610
140
Welding Current(A mps)
140 150 160 170
Welding Current(A mps)
610
620
630
160Welding Speed(mm/min)140
120180
180160
Welding Speed(mm/min)140
200180
Welding Speed(mm/min)
Surface Plot of Tensile Strength
Tensile Strength(MPa)
280
320
360
140 150 160 170
Welding Current(A mps)
400
440
Edge Included A ngle(Deg)4030
180
6050
Edge Included A ngle(Deg)40
7060
Edge Included A ngle(Deg)
Surface Plot of Tensile Strength
Tensile Strength(MPa)
540
560
580
140
Welding Current(A mps)
140 150 160 170
Welding Current(A mps)
580
600
620
Gas Flow Rate(Litres/min)108
180
1412
Gas Flow Rate(Litres/min)10
1614
Gas Flow Rate(Litres/min)
Surface Plot of Tensile Strength
Tensile Strength(MPa)
Sigma Journal of Engineering and Natural Sciences, Research Article, Vol. 39, No. 1, pp. 80-96, March, 2021
93
Figure 12(a). Figure 12(b).
Figure 12(c).
Figure 12. Surface plots for impact strength
From Fig.12(a) it is understood that maximum impact strength is obtained at welding current of 140 Amps
and welding speed of 200 mm/min.
From Fig.12(b) it is understood that maximum impact strength is obtained at welding current of 140 Amps
and edge included angle of 60 Deg.
From Fig.12(c) it is understood that maximum impact strength is obtained at welding current of 140 Amps
and gas flow rate of 16 litres/min.
From surface plots of impact strength (Figure.12), it is understood that maximum impact strength is
obtained at welding current of 140 Amps, gas flow rate of 16 litres/min, welding speed of 200 mm/min and edge
included angle of 60 Deg
70
80
90
140
Welding Current(A mps)
140 150 160 170
Welding Current(A mps)
100
110
160Welding Speed(mm/min)140
120180
180160
Welding Speed(mm/min)140
200180
Welding Speed(mm/min)
Surface Plot of Impact Strength
Impact strength(Joules)
140
Welding Current(Amps)
140150
160170
Welding Current(Amps)
6050
4030
180
70
60
Edge Included Angle(Deg)
Surface Plot of Impact Strength
Impact strength(Joules)
40
50
60
70
80
15
30
45
140
Welding Current(A mps)
140 150 160 170
Welding Current(A mps)
60
75
Gas Flow Rate(Litres/min)108
180
1412
Gas Flow Rate(Litres/min)10
1614
Gas Flow Rate(Litres/min)
Surface Plot of Impact Strength
Impact strength(Joules)
Sigma Journal of Engineering and Natural Sciences, Research Article, Vol. 39, No. 1, pp. 80-96, March, 2021
94
Figure 13(a). Figure 13(b).
Figure 13(c).
Figure 13. Surface plots for maximum bending load
From Fig.13(a) it is understood that maximum value of Max. Bending load is obtained at welding current of
140 Amps and welding speed of 200 mm/min.
From Fig.13(b) it is understood that maximum value of Max. Bending load is obtained at welding current of
140 Amps and edge included angle of 60 Deg.
From Fig.13(c) it is understood that maximum value of Max. Bending load is obtained at welding current of
140 Amps and gas flow rate of 16 litres/min.
From surface plots of Max. Bending load (Figure.13), it is understood that the maximum value (Max.
Bending load) is obtained at welding current of 140 Amps, gas flow rate of 16 litres/min, welding speed of 200
mm/min and edge included angle of 60 Deg.
OPTIMIZATION The optimization is carried out using Response optimizer available in MINITAB statistical software. The
objective is to maximize tensile strength, impact strength and Max. Bending load. From figure.14 it is understood
that at Welding Current of 180 Amps, gas flow rate of 11.6434 litres/min, welding speed of 200 m/min and Edge
Include Angle of 63.8392 Deg, optimal Tensile Strength of 609.9863 MPa, Impact Strength of 88.1070 Joules and
Max. Bending load of 5.1258 KN are obtained.
2.50
2.75
3.00
140
Welding Current(A mps)
140 150 160 170
Welding Current(A mps)
3 .25
3.50
160Welding Speed(mm/min)140
120180
180160
Welding Speed(mm/min)140
200180
Welding Speed(mm/min)
Surface Plot of Max.Bending Load
Max. Bending Load(KN)
5.0
5 .5
6 .0
140
Welding Current(A mps)
140 150 160 170
Welding Current(A mps)
6 .5
7 .0
Edge Included A ngle(Deg)4030
180
6050
Edge Included A ngle(Deg)40
7060
Edge Included A ngle(Deg)
Surface Plot of Max.Bending Load
Max. Bending Load(KN)
4.8
5 .6
6 .4
140
Welding Current(A mps)
140 150 160 170
Welding Current(A mps)
7 .2
8 .0
Gas Flow Rate(Litres/min)108
180
1412
Gas Flow Rate(Litres/min)10
1614
Gas Flow Rate(Litres/min)
Surface Plot of Max.Bending Load
Max. Bending Load(KN)
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95
Figure 14. Optimal solution of Surface Response Method
Validation experiment is performed, as the optimal welding parameters are not within the 31 experiments
presented in Table. Validation experiment is performed at Welding Current of 180 Amps, gas flow rate of 12
litres/min, welding speed of 200 m/min and Edge Include Angle of 64. The measured values of validation
experiments are presented in Table.9.
Table 9. Validation experiment values
Optimal value Experimental value % error
Tensile strength (MPa) 609.9863 602 1.32
Impact strength(Joules) 88.1070 84 4.88
Max.Bending Load (KN) 5.1258 5 2.51
CONCLUSIONS Based on the experiments performed the following conclusions are drawn:
1) Empirical mathematical models are developed for tensile strength, impact strength and maximum
bending load for TIG weld dissimilar joints of AISI 304 and AISI 310 using statistical software by
considering only the significant coefficients.
2) Welding current is the most important parameter which improves the tensile strength, impact
strength and maximum bending load; this is due to higher heat input.
3) Higher flow rate of welding gas along with welding current increases the melting rate filler wire
there by improves the deposition rate.
4) Welding speed plays an important role in deposition rate. Low welding speeds lead to over
melting and higher welding speeds leads to improper penetration of filler metal.
5) Optimal Edge included angle of the weld joint reducing the welding time and improves the weld
joint strength.
6) From the contour plots, it is observed that the most influencing parameter is welding current,
followed by flow rate of gas, fire feed rate and edge included angle.
7) From surface plots, we can get optimal combination of two parameters at a time. From overall
plots for each output response one may conclude that for maximum tensile strength, impact strength and
maximum bending load can be achieved when welding current of 140 Amps, gas flow rate of 16 litres/min,
welding speed of 200 mm/min and Edge Include Angle of 60 Deg.
8) From Response surface optimizer, it is understood that at Welding Current of 180 Amps, gas flow
rate of 11.6434 litres/min, welding speed of 200 mm/min and Edge Include Angle of 63.8392 Deg,
optimal Tensile Strength of 609.9863 MPa, Impact Strength of 88.1070 Joules and Max. Bending load of
5.1258 KN are obtained.
Sigma Journal of Engineering and Natural Sciences, Research Article, Vol. 39, No. 1, pp. 80-96, March, 2021
96
Acknowledgements The authors thank M/s Metallic Bellows (I),Pvt Ltd, Chennai, IITAM University, Visakhapatnam and
GMRIT, Rajam, India for providing the experimental facility.
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